This invention relates to communication antennas and, more specifically, to wideband communication antennas with reduced susceptibility to low angle multipath signal effects.
In many applications it is desirable to provide for RF data link communication over a wide band of frequencies, however, in some instances reception at low elevation angles may be affected by multipath effects, such as surface reflections. Such applications may include low angle communication with ground vehicles and other situations in which the quality of communications may be limited by multipath type fading or effects.
One particular application relates to aircraft carrier-based landing operations. Communications in this environment may be subject to degradation as a result of signal fades caused by sea surface reflections. A relatively wide bandwidth (e.g., 1350 to 1850 MHz) may be employed for the RF data link used for final approach aircraft communications. Reliability and quality of communication in this environment is made more critical in the context of the need for high dependability transmission of position related data to aircraft approaching a landing on the carrier deck. For increased accuracy of use of Global Positioning System (GPS) signals regarding aircraft position relative to the carrier deck, Differential GPS (DGPS) signals can be derived relative to the position of the aircraft carrier and transmitted to an approaching aircraft. In this way, local and other errors inherent in basic GPS signals received by the aircraft can be subjected to in-aircraft correction, by use of DGPS signals, for increased positional accuracy in the landing process. Errors addressed by use of the DGPS signals may include ionospheric, tropospheric and satellite clock and ephemeris errors. DGPS signals appropriate for this use may be provided through implementation of established techniques.
However, for such shipboard DGPS and other applications, available antennas may in operation be subject to signal fades or other degradation of performance due to multipath or other effects, as well as being subject to limitations regarding one or more of bandwidth or other limitations, excessive height or size (e.g., for carrier or vehicle installations) or other shortcomings.
Objects of the present invention are, therefore, to provide new or improved antenna systems and such antenna systems which may provide one or more of broadband operation, reduced size and reliable operation in the presence of multipath or related effects.